1. Field of the Invention
The present invention relates to the manufacture of compositions from cellulose fiber material, the fiber based product, and products containing the fiber based product.
2. Background of the Art
Many food and agricultural byproducts contain substantial amounts of cellulose. Cellulose is known to be useful in a wide range of markets. The food industry uses cellulose as a fat replacement, a component in products such as dietary fiber supplements, suspension agents, emulsifiers, water binding agents, as well as for edible films and coatings. The pharmaceutical industry uses cellulose as a component in bulking agents and dietary fibers for treatment and prevention of coronary heart disease, Type II diabetes, hypertension, diverticulosis, hemorrhoids, obesity, and so forth. Industrial applications of cellulose include use in filter media, latex paint, and so forth.
Native cellulose fibers contain lignin, a polymeric material found in every type of vascular plant. Prior art processes for refining cellulose seek to remove lignin before any substantive treatment of the fibers. Lignin is known to cause cellulose fibers to stick together, thus reducing the surface area available for any subsequent reactions. It is believed that the presence of lignin also reduces the ability of cellulose microfibers to intertwine and entangle, thus reducing the structural integrity and/or strength of the final product.
U.S. Published patent application 0020060382 describes a process for making lyocell fibers comprising the steps of: (a) contacting a pulp comprising cellulose and hemicellulose with an amount of a reagent sufficient to reduce the degree the of polymerization of the cellulose to the range of from about 200 to 1100 without substantially reducing the hemicellulose content of the pulp; (b) reducing the kappa number of the pulp treated in accordance with step (a) to a value less than about 2.0; and (c) forming fibers from the pulp treated in accordance with steps (a) and (b).
The process described by Turbak et al. (U.S. Pat. No. 4,374,702) for preparation of MFC from wood pulp basically involved a homogenization operation, during which wood pulp was repeatedly passed through a high pressure homogenizer until the suspension becomes a substantially stable dispersion. The homogenizer had a small diameter orifice in which the suspension was subjected to a pressure drop of at least 2000 psi and a high velocity decelerating impact against a solid surface. Homogenization is a very efficient process that converts the fibers into microfibrillated cellulose without substantial chemical change of the starting material. The term “without substantial chemical change” means the fact that the cellulosic material is not intended for uniform chemical modification, such as esterification, acidification, substituent addition, massive molecular breakdown and the like. Homogenizing primarily effects a physical size change, with only potentially modest chemical changes occurring incidentally. Finely divided cellulose is also produced in traditional processes used in manufacturing mechanical pulp, fiberboard and paper pulp. However, these traditional processes involve the use of additional chemical treatment to available cellulose pulps, as for example, acid hydrolysis or mercerization, which chemically alter or degrade the prepared cellulose pulps. In the paper industry, it is well known that paper strength is directly related to the amount of beating or refining which the fibers receive prior to formation. However, beating and refining as practiced in the paper industry are relatively inefficient processes since large amounts of energy are expended to gain relatively minor amounts of fiber opening fibrillation.
Lignin removal from cellulose is currently accomplished using extremely high temperatures and pressures. These extreme conditions cause raw material fragments to break apart, thus releasing the desired cellulose-based micro fibers. In addition, the raw materials are subjected to high concentrations of sodium hydroxide. See, for example, U.S. Pat. No. 5,817,381 to Chen, et al. Such a process is extremely energy-intensive in terms of the required temperatures and pressures. Further, the process produces a waste stream regarded as hazardous due to elevated pH levels caused by the use of large amounts of sodium hydroxide. Treatment of the waste stream adds to the cost of production and impacts the overall efficiency of this process.
A recent improvement in that process by Lundberg et al. (U.S. patent application Ser. No. 09/432,945) comprises a method for refining cellulose, the process comprising soaking raw material in NaOH having a concentration of about five (5) to 50% (dry basis) to produce soaked raw material which steeps for about 6 hours to allow the NaOH to work, refining the soaked raw material to produce refined material, dispersing the refined material to produce dispersed refined material, and homogenizing the dispersed refined material to produce highly refined cellulose (HRC) gel having a lignin concentration of at least about one (1)% and a water retention capacity (WRC) of about 25 to at least about 56 g H2O/g dry HRC. The method of the Lundberg et al invention produces a waste stream having a pH within a range of 8 to 9 and a reduced volume as compared to conventional cellulose refining processes.
In one embodiment, the method further comprises draining and washing the soaked raw material until the pH is down to about 8 to 9, bleaching the washed material at a temperature of about 20 to 100° C. in hydrogen peroxide having a concentration of about one (1) to 20% dry basis, and washing and filtering the bleached material to produce a filtered material having a solids content of about thirty percent (30%) The filtered material may be refined by being passed through a plate refiner. The plate refiner essentially breaks up the lignin as it shreds the material into refined cellulose particles. The method of that invention is asserted to be energy efficient because it does not require high pressures and temperatures as in prior art processes. Despite the presence of higher lignin concentrations in the final product, the HRC gel of the Lundberg et al invention has a water holding capacity that is at least as good or better than prior art products. Use of a plate refiner to break up the lignin rather than using high concentrations of NaOH has the added advantage of producing a non-hazardous waste stream having pH within a range of 8 to 9 and a reduced volume.
U.S. Pat. No. 6,083,582 describes a process and materials are described in which highly refined cellulose fibers are broken down into microfibers and further processed into compositions, films, coatings and solid materials which are biodegradable and even edible. The process for the formation of hardenable compositions may comprise providing a composition comprising highly refined non-wood cellulose fiber, mechanically reducing the size of the non-wood cellulose fiber to less than 2 mm, reducing the amount of binding of microfibers by lignin within said non-wood cellulose fibers present in said composition comprising cellulose fiber to form a first fiber product, providing pressure of at least 300 psi to said first fiber product while it is in the presence of a liquid, and removing said pressure within a time interval which will cause said cellulose fiber to break down into a second fiber product comprising microfibers in said liquid. The patent describes edible foodstuff wherein material having nutritional value is coated, wrapped or coated and wrapped with a film of material made from the fibers of the patent.
U.S. Pat. No. 6,231,913 describes a pre-emulsion fiber composition (i.e., the mixture formed from an oil and mixture that can be formed into an oil-in-water emulsion using standard emulsification equipment known by those of skill in the art, such as a high-pressure, ultrasonic, or other homogenizer, a rotator/stator device, and like equipment. The pressure employed, the shear rate, and/or the time of emulsification may vary widely depending upon the particular equipment employed. The pressure employed when homogenizers are used for the emulsification will generally range from about 130 psi to about 220 psi, with about 180 psi being preferred. When equipment other than homogenizers is used for the emulsification, the shear rate employed will generally range from about 9,000 to about 100,000 reciprocal seconds. The emulsification time will generally range from about 1 second to about 10 minutes, but may be higher, depending upon whether the emulsification is performed in a single pass, or in multiple passes, and will more usually range from about 2 seconds to about 30 seconds.
In spite of the improvements in cellulose fiber manufacture and properties that are provided among these various processes and materials can still be improved upon. Additionally, the processes, even if they are improved with regard to their environmental friendliness, it would be desirable if the processes could be further simplified, improved to produce more functional products, and produce fewer and less harmful by-products.